Method for making carbonaceous materials

ABSTRACT

A fluidized bed disproportionation of carbon monoxide is effected using ferrous metal component-containing catalysts in particulate form. The bed also contains an abradant to continuously remove from the surface of those particles a substantial quantity of the carbonaceous fibers formed on those surfaces. The method produces a carbonaceous material of desired carbon and ferrous metal content. The process allows the use of two beds in series for producing high carbon content products.

CROSS-REFERENCES

This application is a continuation of application Ser. No. 620,996 filedJune 15, 1984, now U.S. Pat. No. 4,650,657, which is acontinuation-in-part of application Ser. No. 339,778 filed on Jan. 15,1982, now abandoned, which is incorporated herein by this reference,which is a continuation of application Ser. No. 188,201 filed Sept. 18,1980, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a method for making carbonaceous materialsthat contain one or more ferrous metal components. More particularly,the invention relates to a fluidized bed method for disproportionatingcarbon monoxide using a particulate ferrous group metal componentcatalyst in a fluidized bed that contains a sufficient amount of inertabradant to remove a substantial amount of the carbon formed on thesurface of the particulate catalyst.

U.S. patent application Ser. No. 99,789 filed Dec. 3, 1979, discloses anew family of carbon/metal materials and methods for making them. Theentire disclosure of that application is hereby incorporated in thisapplication by reference. Briefly, that application discloses makingcarbon/metal materials by disproportionating carbon monoxide in thepresence of a ferrous group metal component catalyst which may be ametal, an alloy, a carbide or other metallic substance. As explainedthere, disproportionation means any of the reactions which occur in thepresence of a ferrous group metal to produce carbon from carbonmonoxide, which can be part of a mixture containing hydrogen or othersubstances. The following are typical reactions: ##STR1##

In these processes, carbonaceous material forms on and grows from thecatalyst surface primarily in the form of fibers. Some non-fibrouscarbon can also be present. As disproportionation continues, thesefibers become tangled masses that occupy increasingly larger volumes inthe fluidized bed reactor. Simultaneously, the effective density of thecarbonaceous material produced falls toward the range of about 0.05 toabout 0.7 grams per cubic centimeter.

It is difficult to produce fibrous carbon/metal materials of preselectedproperties in a continuous process. For example, as substantial amountsof carbon deposit on catalyst particles larger than 120 microns, the bedtends to form two substantially distinct parts. The lower part of thebed includes relatively large, partially carburized ferrous group metalcomponent particles. The upper part of the bed includes smaller carbonand ferrous metal component particles that have broken away from thelarger particles in the lower part of the bed. If the bed contains onlycarbon and ferrous metal component catalyst, the bed mass generallybecomes larger than desired, and the ratio of ferrous metal to carbon inthe elutriated product is not easily controlled. Further, if thesuperficial gas velocity is too low, the bed mass can increase until theentire reactor is filled with carbon/metal material, which isundesirable, and can also result in too broad a range of carbon to metalratio in the product, too high a carbon to metal ratio in the product,and too high bulk density of the product. If the superficial gasvelocity is too high, then material can be entrained from the reactorwith a lower than desired carbon to metal ratio.

Other problems can arise as a result of overall or local temperaturefluctuations in the bed. As the bed temperature is increased, the ratioof nonfibrous to fibrous carbon in the carbon/metal product can becomelarger than desired. Control of temperature is difficult because thecarbon deposition process is exothermic, so that in a practicalcommercial system it is necessary to have heat exchange tubes immersedin the fluid bed to provide heat removal to maintain a desired bedtemperature. Low density carbon/metal material can cling to heattransfer surfaces, resulting in an insulating layer being formed on theheat transfer surfaces which prevents adequate heat removal and resultsin an undesirable rise in the bed temperature.

Thus, there is a need for a continuous process for efficiently preparingfibrous carbon/metal materials of preselected properties.

SUMMARY

The present invention satisfies this need. In general, the method of thepresent invention provides for fluidized bed disproportionation ofcarbon monoxide using ferrous metal component-containing catalysts inparticulate form together with a sufficient amount of at least oneabradant to continuously remove from the surface of those particles asubstantial quantity of the carbonaceous fibers formed on thosesurfaces. This method produces a carbonaceous material of a desiredcarbon content and bulk density.

In the process of the present invention, a feed gas containing carbonmonoxide is introduced into a reaction zone having a bed containingparticulate material to form a fluidized bed. The particulate materialcomprises an abradant and a ferrous metal containing catalyst. Thecatalyst catalyzes the disproportionation of at least a portion of thecarbon monoxide of the feed gas to form (i) a reacted gas stream and(ii) a fibrous carbonaceous/ferrous metal material that forms on thesurface of the catalyst. The abradant abrades the fibrouscarbonaceous/ferrous metal material from the surface of the catalyst.The abradant also inhibits carbon/metal material from clinging to heattransfer surfaces and the reactor walls. The feed gas is introduced intothe reaction zone at a sufficient velocity for fluidizing theparticulate material and so that the reacted gas elutriates from thefluidized bed abraded fibrous carbonaceous/ferrous metal material. Thetemperature of the reaction zone is maintained from 300° to 700° C. andthe pressure in the reaction zone is maintained from 1 to about 10atmospheres. Preferably the feed gas is introduced to the reaction zoneat a temperature at least 50° C. less than the reaction zonetemperature, and generally at about 250° C. or less. This reduces theheat load on the heat transfer system and avoids carbon deposition atthe feed gas inlet.

The elutriated fibrous carbonaceous/ferrous metal material is withdrawnfrom the reaction zone. The withdrawn material comprises at least 2% byweight ferrous metal and has a weight average particle size of fromabout 1 to about 50 microns.

Ferrous metal is introduced to the reaction zone for replenishing theferrous metal withdrawn from the reaction zone as part of the fibrouscarbonaceous/ferrous metal material.

In one version of the invention, where a high carbon content product isdesired, the elutriated material from a first fluidized bed can beintroduced into a second fluidized bed for increasing the carbon toferrous metal ratio in the product. If desired, the elutriated productfrom the first bed can be fragmented before it is introduced into thesecond bed for decreasing the bulk density of the carbon/ferrous metalmaterial prior to carbon deposition in the second bed.

As described in detail below, the fibrous materials produced accordingto this fluidized bed process have unique properties, at least partiallyresulting from the ferrous metal content of the material.

This method provides significant advantages in the fluidized beddisproportionation of carbon monoxide. This carbonaceous product canhave a high ratio, 4:1 or even higher, of carbon-to-ferrous metalcomponent. Because the abradant acts first to remove from the catalystsurface the carbon farthest from that surface, the ratio of carbon toferrous metal component in the elutriated carbanaceous product tends tobe substantially higher than where no abradant is used. Further, bypromoting fragmentation of elutriable particles, the abradant controlsthe size of the reactant mass in the bed. In the continuous operation ofthe process, the size of the reactant mass can be minimized, thusminimizing both the reactor volume needed and the pressure drop acrossthe reactor. The abradant also removes carbonaceous material fromreactor surfaces, keeping those surfaces clean. This is most importantat places such as distributor plate orifices, which tend to clog, andheat transfer surfaces.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 schematically shows a single stage process according to thepresent invention and includes an elevation view of a reactor used inthe process;

FIG. 2 schematically shows a modification of the process of FIG. 1 forproducing a high carbon content material;

FIG. 3 schematically shows a two stage process according to the presentinvention and includes an elevation view of a reactor suitable in theprocess;

FIG. 4 schematically shows a modification of the process of FIG. 1 forproducing a relatively low bulk density product;

FIG. 5 schematically shows a modification of the process of FIG. 1, thereactor used having an expanded freeboard section and a lower bubblingbed layer of inert material to enhance reactor performance; and

FIG. 6 shows graphically the results from using a process according tothe present invention.

DESCRIPTION

The present invention a provides a fluidized bed process for preparing apredominantly fibrous carbonaceous/ferrous metal material (also referredto as carbon/metal product). This material comprises from 50 to 98% byweight carbon, from about 2 to about 50% by weight ferrous metal, andfrom about 0.1 to about 1.5% by weight hydrogen. By the term "ferrousmetal" there is meant a metal of Group VIII of the Periodic Table of theElements, such as iron, cobalt, nickel, and combinations, carbides,oxides, and alloys thereof. The fibrous carbonaceous/ferrous metalmaterial includes a major phase and a minor phase, the major phasecomprising from about 95 to about 99.9% by weight carbon, from about0.1% to about 1.5% hydrogen, and the balance, if any, being the ferrousmetal. The minor component is nodules which are dispersed throughout themajor phase and are intimately associated with and at least partlybonded to the carbon in the major phase. The minor phase comprisescarbon and at least 50% by weight ferrous metal.

In the process, a feed gas containing carbon monoxide is introduced intoa reaction zone containing particulate material to form a fluidized bed.The particulate material comprises an abradant and a ferrous metalcontaining catalyst. The catalyst catalyzes the disproportionation of atleast a portion of the carbon monoxide to form (i) a reacted gas streamand (ii) a predominantly fibrous carbonaceous/ferrous metal materialthat forms on the surface of the catalyst. The reacted gas elutriatesthe abraded material from the fluidized bed. The abradant promoteselutriation of the product, enhances heat transfer from the reactor, andhelps provide temperature uniformity within the reactor.

In a first embodiment of this method, the particulate ferrous metalcomponent catalyst and the abradant are separate, discrete particles.The catalyst particles preferably have a mass mean particle size of fromabout 50 to 300 microns. As the catalyst particle size increases, thedensity of the product increases and the carbon content of the productdecreases.

In a second embodiment, the ferrous metal component catalyst isdeposited on, and carried by the abradant particles. Deposition can beeffected by vapor deposition or from a liquid solution. The mass meanparticle size of the catalyst in the second embodiment is less thanabout one micron.

All particle sizes presented herein, whether described as "weightaverage particle size" or "mass mean particle size" are particle sizesas determined by micromerograph or sieve analysis.

Particulate abradant is used with both of these embodiments. Theabradants are preferably inert, i.e. non-catalytic with respect tocarbon deposition. Examples of the abradants useful in this newfluidized bed process are alumina, silica, silicon carbide, andBlastite. Blastite is a sand blasting material composed primarily ofalumina with some iron oxides and other metal oxides. Such abradantshave a density in the range of about 1 to about 4 grams per cubiccentimeter Generally, the abradant constitutes about 10% to about 90% byweight of the solids in the fluidized bed. Preferably, the abradantconstitutes about 2/3 to about 4/5 by weight of the solids in thefluidized bed. The mass mean particle size of the abradant is from about50 to about 300 microns, preferably from about 80 to about 120 microns.

It has been determined that an angular abradant such as angular aluminahaving a weight average particle size of 120 microns and a bulk densityof 1.65 g/cm is a satisfactory abradant. However, small particles ofalumina, i.e. weight average particle size of 9 microns, areunsatisfactory. Similarly, low density particulate material such asspherical silica having a weight average particle size of 67 microns anda bulk density of 0.78 g/cm³ is unsatisfactory.

The abradant helps abrade the carbonaceous/ferrous metal material thatforms on the surface of the catalyst from the catalyst to produce thecarbon/metal product. The abradant also promotes elutriation of theproduct from the bed, enhances heat transfer from the reactor, and helpsprovide temperature uniformity through the reactor.

In the first embodiment, where the ferrous metal catalyst is in the formof discrete particles with a mass mean size larger than 120 microns,then preferably two abradants are used. A second relatively largerabradant is used along with the relatively smaller abradant, the smallerabradant having a mass mean size in the range of from about 80 to about120 microns. The larger size abradant has a mass mean size about equalto the mass mean size of the catalyst and a density at least equal tothat of the smaller size abradant, and preferably has a density of about1.5 times the density of the smaller abradant. The purpose of using alarger, more dense abradant and a smaller, less dense abradant is tomaintain abradant well distributed throughout the entire bed. Whenferrous metal catalyst particles larger than about 120 microns are used,the fluidized bed tends to consist of a lower, denser, ferrous metalrich region, and an upper, less dense, carbon rich region. The larger,denser abradant is present primarily in the lower ferrous metal richregion and the smaller, less dense abradant is present primarily in theupper carbon rich region. When two abradants are used, each abradantcomprises at least 10% by weight of the abradant used in the reactor.

It can be desirable to have a bubble formation zone comprising a thinlayer, typically 10 to 30 cm deep, of inert particulate material at thebottom of the reactor. The particulate material has a mass mean particlesize of from about 200 to 300 microns and a bulk density in the range of1.4 to 4 g/cm³. The particulate material used for the bubbling formationzone can be the same material used for the abradant. Under the desiredoperating conditions, this bottom bubble layer produces gas bubbles inthe range of about 5 to 15 centimeters in diameter. These bubbles breakup upon reaching the carbonaceous upper region of the fluidized bed. Thepurpose of the bubbling layer is to provide agitation to the reactiveportion of the fluidized bed to enhance solids circulation and heattransfer. The lower bubbling layer is most effectively used inconjunction with a flat gas distributor plate.

The new fluid bed process is generally carried out in a temperaturerange of about 300° C. to about 700° C., preferably in the range ofabout 400° C. to about 550° C. The reactor operating pressure is fromabout 1 to about 10 atmospheres.

Contact time of carbon monoxide with catalyst is generally in the rangeof about 1 to about 15 seconds, more preferably in the range of about 8to about 12 seconds.

The superficial velocity of the gas introduced into the reaction zoneneeds to be sufficient to fluidize the bed and to elutriate from the bedthe product carbonaceous/ferrous metal material. More specifically, thesuperficial velocity should be at least 1.5 times, and preferably atleast 2 times, the minimum fluidization velocity of the abradantmaterial or the ferrous metal material used, whichever has the greaterminimum fluidization velocity. The superficial velocity under steadystate conditions provides an entrainment rate of the carbon portion ofthe product which is equal to the deposition rate of the carbon in orderto maintain a constant carbon inventory in the reactor, and to providethe desired ratio of carbon to ferrous metal in the elutriated product.In general, the ratio of carbon to ferrous metal in the product tends todecrease with increasing gas superficial velocity. In addition to therequirement to adequately fluidize the abradant and ferrous metalmaterials, it is also necessary to adequately fluidize the carbon richmaterial. The effective minimum fluidization velocity of the carbon richmaterial is in the range of about 10 to about 15 cm/s (centimeters persecond). It is normally the case that a superficial velocity high enoughto provide adequate product elutriation also provides adequatefluidization of the carbon rich material.

The superficial velocity of the reactants through the fluidized bed isgenerally in the range of about 10 cm/s to about 70 cm/s, morepreferably from about 20 cm/s to about 60 cm/s. The lower part of therange, up to about 40 cm/s, is preferred for production of material withabout 15% or less ferrous metal content, and the upper region, aboveabout 40 cm/s, is preferred for production of material with about 15% ormore ferrous metal content.

In one series of tests it was determined that increasing the superficialvelocity of the feed gas through the reactor from about 32 centimetersper second to about 40 centimeters per second favored production offibrous material, while the lower velocity favored production of agranular, denser form of carbon.

The system design and operating conditions are selected to provide a bedturnover time, which is the ratio of carbon mass in the bed to the rateof carbon deposition, of less than 50 hours, and preferably of less than25 hours. Generally the bed turnover time is in the range of 2 to 50hours, and preferably in the range of 4 to 25 hours. In general, theratio of carbon to ferrous metal in the product increases as theturnover time increases. Product containing in excess of 40% carbon canbe produced in only one hour or less from startup.

The fluidizing agent for this process is a gas mixture whose reactivecomponents are carbon monoxide and hydrogen. When made conventionally,as in coal gasification, such gas mixtures generally also containnonreactive components such as nitrogen. Most commercially available gasfeed streams containing carbon monoxide also contain relatively largeamounts of hydrogen. This process is generally used with feed gasstreams having carbon monoxide to hydrogen molar ratios of at least 1:1,preferably at least 2:1, and generally up to 10:1. The carbon monoxideconcentration at the reactor inlet is at least 15% by volume, andpreferably in the range of 20%-60%.

Preferably the feed gas inlet temperature is at least 50° C. lower thanthe reactor temperature. Generally the feed gas inlet temperature isless than about 300° C., and preferably less than about 250° C., forthree reasons: (i) to avoid deposition of carbon upstream of thereaction zone which can occur at high temperatures; (ii) to avoid localover-heating at the reaction zone entrance; and (iii) to help removeheat of reaction in the vicinity of the reaction zone entrance Thedisproportionation reaction is exothermic, and cooling can be required.If an inlet gas temperature above 250° C. is used, it is important toselect materials that are not catalytic to carbon deposition at the gasinlet. Similarly, all exposed surfaces within the fluidized bed carbondeposition reactor system that are maintained at a temperature above250° C. preferably are non-catalytic with respect to carbon deposition.

Exemplary of suitable catalysts are malleable iron shot, steel shot,atomized steel, and sponge iron. It has been found that sponge iron isactive at disproportionating carbon monoxide at temperatures as low as450° C., while steel shot and atomized steel require temperatures in theorder of about 550° C. Preoxidization of these forms of iron is desiredto enhance reactivity with carbon monoxide. Preoxidization of the ironcan be done in a furnace at about 800° C. for a short amount of time, orby placing the iron in a pan, covering the iron with water, and bakingit at 100 to 120° C. Addition of oxygen equal to about 1% of the mass ofthe iron is desired for these forms of iron which are supplied in anunoxidized state. Preoxidation of iron oxide powder and iron ore powderrich in iron oxides is not necessary, of course, since the iron isalready primarily or entirely in an oxidized state.

Detailed disclosure of the disproportionation process and catalystsuseful therefor appears in U.S. patent application Ser. No. 99,789 filedDec. 3, 1979. In the preferred embodiment of that application, as here,the particulate catalyst is iron, iron oxide or iron ore. To obtainmaximum carbon content in the product, the catalyst is preferably in aform having good structural integrity. Iron powders are examples ofcatalysts having good structural integrity, and iron oxide is an exampleof a catalyst having poor structural integrity

The configuration of the reactor plays an important role in achievingdesired product properties, and can vary according to the applicationand operating conditions. The reactor consists of a section containing afluidized bed, a freeboard section above the fluidized bed, and a gasdistribution entrance section. The section containing the fluidized bedalso contains one or more heat transfer tube arrays to remove the heatof reaction from carbon deposition. The height of the fluidized bedsection is from about 2 to about 20 meters, more preferably from about 4to about 10 meters. The height of the freeboard section is from about 2to about 10 meters, more preferably from about 4 to about 6 meters. Theheight to diameter ratio of the fluidized bed section is from about 1:1to about 40:1, more preferably from about 4:1 to about 20:1

In its simplest form, the reactor can be a right circular cylinder.Depending on the application, it can be desirable to have a reactorwhere the fluid bed portion is divided into a lower, smaller diametersubsection and an upper, larger diameter subsection. This configurationcan be particularly useful when a ferrous metal catalyst with mass meanparticle size above about 120 microns is used, where the lower, smallerdiameter portion is comprised mainly of ferrous metal catalyst andrelatively larger, denser abradant, and the upper, larger diameterportion is comprised mainly of carbon rich carbonaceous/ferrous metalmaterial and relatively smaller, less dense abradant.

In some cases, it can be desirable to have the freeboard section be oflarger diameter than the fluid bed portion to maintain the elutriationrate at a reasonable level. This configuration can be particularlyuseful when the feed gas has a low concentration of carbon monoxide,which tends to promote an entrainment rate that can be significantlyhigher than the carbon deposition rate.

In yet other cases, it can be desirable to have carbon deposition in twosuccessive reactors, where the material elutriated from the firstreactor is fed to a second reactor and further carbon deposition takesplace to increase the product carbon to metal ratio. This configurationcan be particularly useful for producing material with a very highcarbon to ferrous metal ratio, especially when a very low bulk densityis required

For example, if the carbon content of the product is lower than desired,i.e. from about 70% to 80% rather than 90%, its carbon content can beraised in a second stage. The elutriated product from the first stagecan be reacted with additional carbon monoxide and hydrogen in a secondfluidized bed that contains little or no free catalyst. In this secondstage, the ferrous metal component catalyst bound in the product fromthe first stage catalyzes the disproportionation, resulting in a productof higher carbon content. If the second stage reaction does not proceedat a satisfactory rate, additional particulate catalyst can be added,either in supported or unsupported form, to produce a product having 90%carbon content or higher.

It is important that the product produced in the fluidized bed containat least 2% ferrous metal. Such a material is useful for manyapplications in which a ferrous metal free material is not suitable.Table 1 presents the ferrous metal content, mass mean particle size, andbulk density of exemplary carbon/metal materials that can be produced bya process according to the present invention. Such carbon/metalmaterials can be used as a magnetic toner in xerography or as a catalystfor catalyzing ferrous group metal-catalyzed chemical reactions.

FIGS. 1-5 show reactor configurations and processes applicable to thepresent invention. FIG. 1 shows a configuration that can be used toproduce a carbon/metal product with metal content from about 10% toabout 50%. The fluidized bed reactor 1 includes a gas inlet 2 for thecarbon monoxide containing gas, a gas distributor 3, and an overheadoutlet 4 for exhaust of the product solids and the depleted gas. Thelower portion of the reactor is occupied by a fluidized bed 5, whichcomprises ferrous metal, abradant, carbon, and hydrogen. Above thefluidized bed is a freeboard region 6. Product particles pass throughthe freeboard region 6 and exit the reactor 1, while abradant andferrous metal particles which are carried into the freeboard region 6preferentially fall back into the fluidized bed 5 due to their higherweight to drag ratio. Immersed in the fluidized bed 5 is a heat transfertube array 7 with an inlet 8 and an outlet 9 for a heat transfer fluid.Steam is a preferred heat transfer fluid. A port 10 is provided for theintroduction of ferrous metal material to compensate for that elutriatedas product. Under steady state operating conditions, the top of thefluidized bed is at the same height as the top of the heat transfer tubearray. The abradant in the fluid bed portion is well distributed to keepthe carbon rich material from clinging to the heat transfer surfaces andinhibiting heat removal.

In operation, the process generally starts with a bed of ferrous metaland abradant particles. The carbon monoxide-containing gas entersthrough the inlet 2, passes through the gas distributor 3, fluidizes thebed portion 5, and provides carbon monoxide for disproportionation tocarbon and carbon dioxide. The initial bed of abradant and ferrous metaloccupy a small portion of the reactor and do not fully cover the heattransfer tube array. As carbon is deposited, the bed mass increases, theaverage bed density becomes lower due to the deposition of relativelylow density carbon, and the bed volume increases. Under steady stateconditions, the bed has grown to the point where the heat transfer array7 is immersed, the elutriation rate of carbon is equal to the depositionrate, and makeup ferrous metal is fed to the reactor at a rate equal tothe elutriation rate of ferrous metal in the product. The depleted gasand entrained product leave the reactor through the outlet 4 and passthrough one or more cyclones 11 in which part of the product isseparated from the gas stream and collected in a first storage container12. The gas and remaining entrained solids then proceed to a bag housefilter 13 where the remaining solids are removed from the gas stream andcollected in a second storage container 14. The particle free depletedgas then proceeds through an exhaust line 15.

FIG. 2 shows a reactor configuration 101 particularly suited forproduction of a high carbon content version of product B of Table 1, theproduct having a ferrous metal content of from about 3% to about 15%. (Alow carbon content version product B of Table 1 can be produced with thereactor configuration of FIG. 1). The two-level fluidized bed reactor101 includes a gas inlet 104 for a carbon monoxide containing gas. Thefeed gas enters the lower and upper segments of the reactor throughlower and upper gas distributors 105 and 106. A lower portion 102 of thefluidized bed contains predominantly larger abradant and ferrous metalrich carbon/metal material. Carbon rich material breaks off from theferrous metal particles and is carried into the upper portion 103 of thefluidized bed, which contains predominantly smaller abradant and carbonrich carbon/metal material. The lower 102 and upper 103 portions of thefluidized bed contain heat transfer tube arrays 107 and 110,respectively, with inlets 108 and 111, respectively, and outlets 109 and112, respectively. Makeup ferrous metal particles are fed to the lowerportion 102 of the fluidized bed by means of a feed port 120. Above theupper fluidized bed section 103 is a freeboard section 113, throughwhich the depleted gas and product material passes on the way to anoutlet line 114.

In operation, the process starts with the lower portion 102 of the bedcontainin9 ferrous metal particles and abradant particles, each having amass mean size in the range of about 120 to 300 microns. The carbonmonoxide containing gas enters through the inlet line 104, passesthrough the lower gas distributor 105, and fluidizes the lower portion102 of the bed. The upper portion 103 of the bed initially contains onlysmaller abradant with a mass mean size of from about 80 to about 120microns. It is fluidized by the gas leaving the lower portion 102 and bysecondary gas entering through the upper level gas distributor 106. Thesecondary gas helps maintain a substantially constant superficialvelocity through the reactor. As carbon is deposited in the lowerportion 102, carbon/ferrous metal particles break off and are carriedinto the upper portion 103 where additional carbon deposition occurs.The gas superficial velocity in the upper portion 103 is at least equalto the superficial velocity in the lower portion 102, and can be up toabout 50% higher, to minimize backmixing of upper portion material intothe lower portion. The lower heat transfer array 107 is fully immersedin the bed at all times. The upper heat transfer array 110 is partiallyimmersed in the bed at the beginning of the operation prior to carbondeposition, and is fully immersed under steady state conditions. Theupper portion 103 of the bed increases in volume as additional carbon isdeposited until steady state equilibrium conditions are reached. Understeady state conditions, the upper heat transfer array 110 is justcovered by the upper fluid bed portion 103, the entrainment rate of thecarbon portion of the carbon/metal product is equal to the carbondeposition rate, and the entrainment rate of the metal portion of thecarbon/metal product is equal to the makeup rate of ferrous metal fedthrough the makeup feed port 120.

Operating conditions and materials are selected to provide a productwith an average ferrous metal content of between about 3% and 15%, asdesired. The elutriated product and depleted feed gas pass through thefreeboard section 113 and exit the reactor through the outlet line 114.Part of the solid product is separated from the gas stream in a cyclone115 and collected in a container 116, while the remaining solids areseparated in a bag house filter 117 and are collected in a secondcontainer 118. The particle free depleted gas stream then exits throughan exhaust line 119. The reactor configuration shown in FIG. 2 is wellsuited for producing product B of Table 1, but can also be useful forproduction of products C and D of Table 1.

FIG. 3 shows a two stage process which is particularly useful forproduction of products C and D of Table 1. It can also be used forproduction of a low metal content version of Products A and B. A firststage reactor 201 is similar to and contains the same general componentsas the reactor 1 in FIG. 1, including a heat transfer array 205 with aninlet 206 and an outlet 207. The partially depleted gas and entrainedsolids from the first stage reactor 201 exit through a transfer line 209and enter a second stage reactor 210 through an injection nozzle 212.The nozzle 212 assures good distribution in the second bed 211 in thesecond stage reactor 210 without clogging and prevents backflow into thetransfer line 209. The second stage reactor 210 is also fed by freshcarbon monoxide containing gas through a feed line 202, the gas enteringthe bed through a distributor plate 213.

In operation, feed gas enters the first stage reactor 201 through thefeed line 202 and a distributor plate 203. The fluidized bed 204 in thefirst stage reactor 201 initially contains abradant particles andferrous metal. The metal can be in the form of separate particles, canbe attached to the abradant, or can be mixed with previously producedcarbon/ferrous metal product. The bed solids consist of carbon,abradant, and ferrous metal. Under steady state conditions, thefluidized bed 204 just covers the heat transfer array 205. The removalrate of the carbon component by elutriation is equal to the rate ofcarbon deposition and the rate of carbon fed as a catalyst carrier, ifany. The removal rate of the ferrous metal component by elutriation isequal to the rate of metal makeup through a feed port 224. Thecarbon/ferrous metal material transferred by entrainment from the firststage reactor 201 to the second stage reactor 210 typically has a metalcontent in the range of about 6% to about 20%, depending on operatingconditions and catalyst form.

In the second stage reactor, additional carbon is deposited to reducethe metal content to about 2% to 10%, depending on the desired finalmetal content. The second stage fluidized bed 211 comprises abradant andcarbon/ferrous material. At steady state, the fluidized bed 211 justcovers the heat transfer array 214 in the second stage reactor 210. Therate of entrainment of the carbon component through an outlet line 218from the second stage is equal to the sum of the carbon feed ratethrough the transfer line 209 and the carbon deposition rate. The rateof entrainment of the ferrous metal component is equal to the feed rateof the ferrous metal component through the transfer line 209. Uponexiting the second stage reactor, the depleted gas stream and entrainedproduct enter a cyclone 219 where some of the product solids areseparated and collected in a first container 220. The gas and remainingentrained solids enter a bag house filter 221 where the remaining solidsare removed and collected in a second container 222. The particle freedepleted gas then exits through an exhaust line 223. For thisconfiguration, the second stage reactor 210 preferably has a diameterbetween 1.2 and 3 times, and preferably between 1.4 and 2 times, thediameter of the first stage reactor 201.

FIG. 4 shows a variation on the configuration in FIG. 3. Theconfiguration in FIG. 4 is particularly useful for production of ProductA with ferrous metal contents from about 3% to about 10%. It is similarto the configuration in FIG. 3 except for the mode of solids transferbetween the first stage reactor 201 and the second stage reactor 210. Inthis case, the depleted feed gas and entrained solids from the firststage reactor 201 pass through a cyclone 304 and a bag house filter 306to separate the solids from the depleted gas stream, which exhauststhrough an exit line 308. The bag house material is periodicallycollected in a lock hopper 307. Solids from the lock hopper 307 and thecyclone 304 are discharged into a transfer line 305 and fed into thesecond stage reactor 210. Passing the solids through the cyclone 304 hasthe effect of fragmenting the particles and significantly decreasing thebulk density of the carbon/ferrous metal material prior to second stagecarbon deposition.

In operation, the reactor system in FIG. 4 is very much like that inFIG. 3. Reactor internal details are similar. The first stage fluid bedreactor is fed by the gas inlet line 302. Makeup catalyst is addedthrough the feed port 224. Depleted gas and first stage entrained solidsexit the reactor through the exhaust line 303. The solids are separatedfrom the depleted gas stream in the cyclone 304 and the bag house filter306, and the particle free depleted gas exhausts through a gas line 308.The bag house 306 periodically discharges solids into the lock hopper307. The lock hopper and cyclone feed solids pass through the transferline 305 to the second stage reactor 210, preferably near the bottom ofthe bed. The second stage reactor 210 uses gas from the feed line 202.The depleted second stage gas and entrained solids pass out of thereactor 210 through line 218 and the cyclone 219, where a portion of thesolid product is collected in the first container 220. The gas andremaining solids pass into the bag house filter 221 and the remainingsolids are collected in the second container 222. The particle freedepleted gas exits through line 223.

The mode of solids transfer between the first and second stage reactorsshown in FIG. 4 is preferred to that shown in FIG. 3 when a low bulkdensity product, such as a product with a bulk density below 0.15 g/cm³,is desired. It can also be preferred when a high carbon monoxideconversion efficiency, such as greater than 80%, is obtained in thefirst stage reactor, and the gas is of little further value for carbondeposition.

Rather than using a cyclone, if it is desired to transfer both gas andsolids from a first stage reactor to a second stage reactor and furtherto reduce the bulk density of the solid particles between stages, thiscan be done by accelerating the particle laden gas stream between thestages, impacting it on a solid plate or series of plates. This has theeffect of fragmenting the particles and decreasing their bulk density,re-entraining the solids, and completing the transfer.

FIG. 5 shows a fluid bed reactor 401 with a lower fluidized bed portion404 and an upper expanded freeboard section 405 for entrainment controlpurposes. The reactor components and functions upstream and downstreamof the freeboard section 405 are as described correspondingly in FIG. 1.The expanded freeboard section 405 lowers the entrainment rate from therate that occurs when a nonexpanded freeboard section is used. Theexpanded freeboard section 405 is particularly useful when a highfluidization velocity is desired in the fluidized bed portion 404 of thereactor 401, and/or when the concentration of carbon monoxide in thefeed gas is low. An expanded freeboard section can be used on either afirst or second stage reactor, or both. The diameter of the expandedsection 405 is preferably from about 1.2 to about 2 times the diameterof the bed section 404.

Any of the reactors shown in the Figures, including the fluid bedreactor 401 can include a bubbling bottom layer of inert particulatematerial to agitate the carbon deposition section of the fluidized bed404. Gas entering from the feed line 402 through the gas distributor 403fluidizes the lower 404A and upper 404B portions of the fluid bed. Thelower portion 404A contains inert particles, preferably with a bulkdensity of from about 1.8 to about 4 g/cm³ and a mass mean particle sizeof from about 200 to about 400 microns. The upper portion 404B containsa smaller abradant, preferably with a bulk density of from about 1.2 toabout 1.8 g/cm³ and a mass mean particle size of from about 80 to about120 microns, ferrous metal catalyst, preferably with mass mean particlesize below 100 microns, and deposited carbon. The two regions do nottend to mix. The gas superficial velocity in the reactor should be atleast 1.5 times the minimum fluidization velocity for the lower layerinert material. When the bed is fluidized, gas bubbles are produced inthe lower portion 404A, and rise up and dissipate into the upperportion. The bubbles have the effect of enhancing solids motion in theupper portion 404B, which in turn enhances heat transfer to the heattransfer array 110, minimizes the possibility of unfluidized sectionsoccurring in the reaction zone, and enhances gas/solid contact, all ofwhich have a positive effect on the process.

Operating and product data for the depicted reactor configurations issummarized in Tables 1-4. Table 1 identifies four product forms.

Table 2 presents the preferred process operating parameters for eachproduct form: temperature, pressure, and gas superficial velocity.Products A and C are preferably made in a two stage process, whileProducts B and D can be made in either a one or two stage process.

Table 3 presents usable catalyst forms for each product, and thepreferred size range. The catalysts fall into tWo broad categories:supported and unsupported. Supported catalysts are very fine, submicronforms which use abradant or carbon as a support. The unsupportedcatalysts are in a larger size powder form.

Table 4 presents abradant data. Abradant in the size range of 80-120microns is always desired in second stage reactors and in the carbonrich regions of first stage reactors. Larger abradant, in the 120-300micron range, is needed in addition to the 80-120 micron abradant infirst stage operation when ferrous metal catalyst in the 120-300 micronsize range is used. In either first or second stage operation, largeinert particles in the 200-300 micron range can be used as a lowerbubbling layer to provide bed agitation.

                  TABLE 1                                                         ______________________________________                                        Product Parameters                                                                   Ferrous        Mean Particle                                                                             Bulk                                               Metal Content  Size*       Density                                     Product                                                                              (% Weight)     (Microns)   (g/cm.sup.3)                                ______________________________________                                        A      3-10           1-10        .05-.25                                     B      3-60           5-50        .10-.7                                      C      2-5            5-50        .15-.3                                      D      3-10           5-50        .1-.3                                       ______________________________________                                         *as determined by micromerograph                                         

                  TABLE 2                                                         ______________________________________                                        Process Parameters                                                                    Reactor    Reactor   Superficial                                              Temperature                                                                              Pressure  Velocity*                                                                             Number                                   Product (°C.)                                                                             (atm)     (cm/s)  Of Stages                                ______________________________________                                        A       400-470    1-10      15-40   2                                        B       450-550    1-10      20-70   1 or 2                                   C       400-550    1-10      30-60   2                                        D       400-550    1-10      30-60   1 or 2                                   ______________________________________                                         *based on 1.2 atmosphere operating pressure and reactor temperature      

                  TABLE 3                                                         ______________________________________                                        Catalyst Parameters                                                                                  Mean Catalyst Size                                     Product     Catalyst Type                                                                            (Microns)                                              ______________________________________                                        A           1, 2, 3    <1                                                                 4          10-100                                                 B           4, 5, 6, 7 10-120                                                             4, 5, 6, 7 120-300                                                C           1, 2, 3    <1                                                                 4, 5, 6, 7 10-120                                                             4, 5, 6, 7 120-300                                                D           1, 2, 3    <1                                                                 4, 5, 6, 7 10-120                                                             4, 5, 6, 7 120-300                                                ______________________________________                                         CATALYST TYPES SUPPORTED                                                      1. metal powder, e.g. submicron iron oxide                                    2. from liquid solution, e.g. ferrous nitrate                                 3. from gas phase, e.g. iron pentacarbonyl                                    UNSUPPORTED                                                                   4. sponge iron powder                                                         5. atomized steel powder                                                      6. iron shot                                                                  7. iron ore                                                              

                  TABLE 4                                                         ______________________________________                                        Preferred Abradant and Bubble Layer Particle Parameter                        Type of                Mean Particle Size                                     Use         Particle   (microns)                                              ______________________________________                                        A           1, 2, 3, 4  80-120                                                B           1, 2, 3, 4,                                                                              120-300                                                C           1, 2, 3, 4, 5, 6                                                                         200-300                                                ______________________________________                                         Type of Use                                                                   A. First stage, second stage reaction zones                                   B. First stage metal rich reaction zone when mean catalyst size exceeds       120 microns                                                                   C. Lower bubbling region to provide bed agitation                             Type of Particle                                                              1. Angular Alumina                                                            2. Angular Silica                                                             3. Angular Silica Carbide                                                     4. Angular Blastite                                                           5. Round Alumina                                                              6. Round Silica                                                          

EXAMPLES Example 1 Run 1

Advantages of the use of an abradant were evident from a series of runsconducted in a fluidized bed reactor which was cylindrical in shape,with an inside diameter of 10 centimeters and a height of 5 meters. Intothis reactor there was placed a reactant mass of 2,500 grams of spongeiron powder having a size range of about 190 to about 260 microns. Theiron particles had been partially oxidized to produce an initiallyoxidized total mass of 2,850 grams. After raising the reactortemperature to about 470° C., by means of external heaters, a gaseousmixture comprising 28% carbon monoxide, 15% hydrogen, and 57% nitrogenon a dry gas molar basis was passed through the reactor. During thefirst run only, the gas mixture also contained about 3% water vapor byvolume. The volumetric gas flow through the fluidized bed was 1.07standard liters per second (2.27 standard cubic feet per minute). Thesuperficial velocity of the gas was 30 cm/s. The nominal bed temperaturewas 470° C.; the nominal pressure, 864 torr (16.7 psia).

During carburetion runs, solid carbon was deposited in the bed throughdisproportionation of the carbon monoxide in the feed gas. Solidmaterial, in the form of carbon/ferrous metal component fragments, wasremoved from the bed by elutriation. The solid material was then removedfrom the gas stream by inertial means and by filtration. The collectedsolid material constituted the product of the carburetion reaction.During the first run, which lasted for about 10 hours, a total of about1,842 grams of carbon was deposited in the bed. At the end of the run,the collected product had a mass of 417 grams and a carbon-to-iron ratioof 1.50/1.

Run 2

In a second run, the material left in the bed at the end of the firstrun was used. The second run was at the same temperature, pressure,volumetric flow and superficial velocity as run 1 except that watervapor was not used. The run lasted about 7 hours; a total of 1,305 gramsof carbon deposited in the bed. To increase product collection rate, thenitrogen flow rate was periodically increased substantially for shorttime periods to increase the elutriation rate. As a result, the bed massat the end of the run had decreased to about 3,712 grams (from 4,073grams). The collected product mass weighted 1,657 grams, and the producthad a carbon-to-iron ratio of 2:1.

Run 3

In a third run, the material left in the bed at the end of the secondrun was used. The same conditions as the second run were used, includingthe periodic nitrogen flow increases. The run time was about 6.5 hours,and the final bed mass was 3,710 grams, which was virtually identical tothe final bed mass from run 2. A total of 1,407 grams of carbon weredeposited in the bed, and 1,418 grams of product, with a carbon-to-ironration of 2.23/1 were collected. During the run, the pressure dropacross the gas distributor plate at the bottom of the bed increasedrapidly, indicating clogging of the orifices in the plate.

Run 4

Before beginning a fourth run, 1,945 grams of alumina having a sizerange of about 260 to about 390 microns were added to the bed materialleft in the reactor after run 3. Run 4 was carried out at the sameconditions as runs 2 and 3. Run 4 lasted for about 3 hours. A total of620 grams of carbon deposited during this run. The rate of nitrogen flowwas not increased at any time during this run. A total a 2,004 grams ofproduct were collected. The product contained no alumina because all thealumina remained in the bed. The carbon and ferrous metal componentdropped to 2,326 grams. The product had a carbon-to-iron ratio of2.70:1. The pressure drop across the distributor plate was substantiallyhigher at the beginning of run 4 than at the end of run 3. Apparently,because the alumina was added from about three meters above the plate,the effect was to drive the reactant mass into the plate orifices,worsening the clogging problem observed during run 3.

Run 5

Run 5 started with the bed material left after run 4 and was performedunder the same conditions as runs 2-4. Again, the rate of nitrogen flowwas not increased at any time during this run. The pressure drop acrossthe distributor plate increased, but at a lower rate than in run 2. Therun time was about 7 hours. A total of 1,040 grams of carbon wasdeposited. A total of 947 grams of product were collected. The endingreactant mass in the bed was 2,419 grams. The carbon-to-iron ratio ofthe product was 4.88:1, a large increase from earlier runs.

Run 6

Run 6, the last in the series, started with bed material left from run 5and was performed under the same conditions as runs 2-5. Again, the rateof nitrogen flow was not increased at any time during this run. Thepressure drop across the distributor plate fell below the pressure droplevel present just after alumina was added. The final pressure drop wasabout half the maximum pressure drop attained during run 5. The runlasted about 5 hours. The mass of carbon deposited was 652 grams. Theproduct mass was 1,163 grams, leaving a reactant mass in the bed of1,908 grams. The carbon-to-iron ratio of the product material was5.67:1.

As these data, set forth graphically in FIG. 6 show, the addition ofalumina to the fluidized bed greatly increased the relative carboncontent of the product, and reduced the reactant mass in the bedsubstantially without requiring periods of high flow. The data trendfrom runs 1 and 2 indicates that, if alumina had not been added to thereactor before run 3, the expected carbon-to-iron ratios for runs 4 and5 product material would be about 2.33:1 and 2.57:1, respectively.Instead, those ratios were 4.88:1 and 5.67:1, respectively. Therefore,the observed carbon-toiron ratio in the products was about twice whatwas expected without alumina.

Example 2

In a second series of some 10 runs under the same conditions as thefirst series (Example 1), the change in product carbon-to-iron ratiowas, for the first 6 runs of this second series, similar to thatobtained in the first 6 runs of the first series. However, the productfrom the last run in this second series had a carbon-to-iron ratiogreater than 15 to 1. Cumulative run time for this second series wasabout 70 hours.

Example 3

In a third series of runs, a mixture of the products from runs 3 to 6(Example 1) in the first series was combined, with about 1,350 grams ofalumina having a size range of about 260 to about 390 microns added. Nopreviously uncarburized ferrous metal component was present during thisthird series. The ferrous metal component bound in the reactant carboncatalyzed disproportionation during this third series.

The disproportionation in this third series took place with a gasmixture including 50% carbon monoxide, 40% nitrogen and 10% hydrogen.The superficial gas velocity through the reactor was 20 centimeters persecond. The operating conditions were otherwise the same as in the firstseries.

During this third series, elutriated products were recycled to thereactor for the first 20 hours of operation. At the end of 20 hours, thecarbon-to-iron ratio in the product reached about 30:1. For the last 22hours of operation, recycling was discontinued, but this highcarbon-to-iron ratio in the elutriated product was maintained.

Example 4

A 290 hour carbon production run series took place over a three weekperiod in a 16 cm diameter, 5 meter tall reactor. Operating conditionsand results are presented in Table 5. The run began with a bedconsisting of 1.5 kg of preoxidized atomized steel powder with a weightaverage particle size of about 250 microns and 2.5 kg of angular aluminaabradant with a weight average particle size of about 350 microns. Anadditional 2.5 kg of alumina was added 72 hours into the run. The feedgas mixture was relatively lean in nitrogen during the first 80 hours topromote catalyst reactivity, and then gas flow conditions were heldconstant as shown in Table 5 for the remainder of the run. Makeup ironwas added periodically to maintain an average iron inventory of about 3to 4 kilograms in the bed. The rate of carbon deposition stayedgenerally constant after the first 30 hours of operation, and theproduct carryover rate stayed fairly constant after the first 100 hoursof operation.

                                      TABLE 5                                     __________________________________________________________________________    Conditions and Results                                                        For Example 4 Run Series                                                                            Carbon                                                  Superficial                                                                            Iron                                                                              Carbon                                                                            Abradant                                                                           Deposition                                                                          Product                                                                            Product Properties                           Time                                                                             Velocity                                                                            In Bed                                                                            In Bed                                                                            In Bed                                                                             Rate  Rate     Bulk Density                             (hr)                                                                             (cm/s)                                                                              (kg)                                                                              (kg)                                                                              (kg) (g/hr)                                                                              (g/hr)                                                                             % Iron                                                                            (g/cm.sup.3)                             __________________________________________________________________________    Start                                                                            --    1.5 0   2.5  --    --   --  --                                        40                                                                              20.7  1.2 8.5 2.5  410   140  10  .28                                       80                                                                              32.2  3.2 20.6                                                                              5.0  470   310   5  .37                                      120                                                                              32.2  2.5 21.1                                                                              5.0  430   430   6  .36                                      160                                                                              32.2  3.7 22.2                                                                              5.0  340   380  10  .24                                      200                                                                              32.2  3.8 23.8                                                                              5.0  430   390  11  .24                                      240                                                                              32.2  4.1 28.1                                                                              5.0  440   380  11  .30                                      280                                                                              32.2  2.8 32.6                                                                              5.0  420   420   9  .36                                      __________________________________________________________________________     Temperature: 550° C.                                                   Iron: Atomized steel, 250 microns                                             Abradant: Angular alumina, 350 microns                                        Gas Composition: 27% CO, 12% H.sub.2, 61% N.sub.2 After 72 hours              Total Product:                                                                 128 kg                                                                       99 kg overhead                                                                29 kg in bed, granular                                                   

A continually increasing mass of carbon in the reactor, especiallyduring the last 100 hours, shows that an equilibrium condition wherecarbon was elutriated from the reactor at a rate equal to the depositionrate was not achieved. At the end of the run when when the bed wasemptied, the contents were found to be predominantly hard, sphericalcarbon/iron granular with an average size of about 180 microns, a bulkdensity of about 0.7 g/cm³, and an iron content of about 4%. This is incontrast to the relatively fibrous material elutriated from the reactoras shown in Table 5. Of the 128 kg of carbon/iron material producedduring the series, about 23% was in the large, hard, dense granularform.

Example 5

Another production run series lasting 340 hours was conducted in an 11centimeter diameter, 3.7 meter tall reactor. Operating conditions andresults are presented in Table 6. In this run series, the problemsassociated with the series described in Example 4 were solved. The runbegan with a bed consisting of 1.2 kg of preoxidized iron shot with aweight average particle size of about 250 microns and 1.5 kg of angularalumina abradant with a weight average particle size of about 350microns. An attempt was made early in the run to achieve a carbondeposition at 470° C. After about 75 hours, the temperature was raisedto 540° C. and maintained there for the duration of the run series. Thegas composition was maintained at 50% N₂, 30% CO, and 20% H₂ after aboutthe first 33 hours of operation. The carbon deposition rate stayedgenerally constant at about 180 g/hr over the last 240 hours of theseries.

                                      TABLE 6                                     __________________________________________________________________________    Conditions and Results                                                        For Example 5 Run Series                                                                            Carbon                                                  Superficial                                                                            Iron                                                                              Carbon                                                                            Abradant                                                                           Deposition                                                                          Product                                                                            Product Properties                           Time                                                                             Velocity                                                                            In Bed                                                                            In Bed                                                                            In Bed                                                                             Rate  Rate     Bulk Density                             (hr)                                                                             (cm/s)                                                                              (kg)                                                                              (kg)                                                                              (kg) (g/hr)                                                                              (g/hr)                                                                             % Iron                                                                            (g/cm.sup.3)                             __________________________________________________________________________    Start                                                                            --    1.2 0   1.5  --    --   --  --                                        40                                                                              36    2.3 0.4 1.5  100   150  18  .14                                       80                                                                              39    2.7 3.3 1.5  170    90  11  .18                                      120                                                                              39    2.6 4.3 1.5  180   160  10  .20                                      160                                                                              42    2.0 6.3 1.5  240   230   9  .26                                      200                                                                              47    0.8 3.4 4.0  180   440   9  .26                                      240                                                                              47    1.2 4.4 4.0  150   160   8  .26                                      280                                                                              47    2.3 4.6 4.0  180   190  11  .16                                      320                                                                              47    1.5 4.2 4.0  180   210   9  .18                                      __________________________________________________________________________     Temperature: 470° C. initial, 540° C. after 75 hours            Iron: Iron shot, 250 microns                                                  Abradant: Angular alumina, 350 microns (initial) Angular silicon carbide,     120 microns (added after 182 hours)                                           Gas Composition: 30% CO, 20% H.sub.2, 50% N.sub.2 After 33 hours              Total Product:                                                                56 kg                                                                         53 kg overhead                                                                3 kg in bed, granular                                                    

Makeup iron was added periodically to maintain an iron inventory in thebed of about 2 kg. The carbon inventory in the reactor increasedsteadily during the first 180 hours of operation. At hour 182, 2.5 kg ofangular silicon carbide with a bulk density of about 1.4 g/cm³ and aweight average particle size of 120 microns was added to the reactor. Inaddition, the superficial gas velocity was increased to 47 cm/s, whereit was held for the remaining 160 hours of the run. The combination ofabradant and higher velocity quickly reduced the mass of carbon in thereactor, and allowed an equilibrium bed mass to be achieved, as thecarbon inventory in the bed stayed essentially constant during the last100 hours of the run. Also, the bulk density of the product was observedto decrease during the latter part of the run. When the bed was emptiedfollowing the run, only a small amount of granular carbon/iron materialwas found, and constituted only about 5% of the total material produced,as opposed to the 23% granular content noted in Example 4.

Example 6

Presented below are test conditions and results for a test run toproduce a high metal content, high bulk density material. Testing wasperformed in the same 11 cm diameter reactor used for the testing inExample 5.

Operating Conditions

Temperature: 470° C.

Superficial Velocity: 63 cm/s

Run Time: 98 hours

Gas Composition: 33% CO, 6% H₂, 61% N₂

Catalyst: Sponge iron, 200 micron mean size, 3 kg initial mass

Abradant: Angular alumina, 350 micron mean size, 2 kg

Product

Total mass: 22 kg

Average Iron Content: 43%

Average Bulk Density: 0.5 g/cm³

In this run, a combination of a friable catalyst form and a high gasvelocity resulted in production of material that was elutriated from thereactor before it had an opportunity to achieve a high carbon content.

Example 7

Two runs were performed in a two stage mode to produce a high carboncontent, low bulk density carbon/iron material. The runs were too shortto establish steady state conditions such as those achieved in Example5, but were of sufficient length to illustrate the concepts involved.Both runs were performed in the 16 cm diameter reactor used in Example4.

First Stage Operating Conditions

Temperature: 470° C.

Run Time: 25 hours

Catalyst: Preoxidized sponge iron, 120 micron mean size, 5 kg mass

Abrandant:

5 kg angular alumina, 260 micron mean size

5 kg angular alumina, 120 micron mean size

    ______________________________________                                        Time Into Run,                                                                           Gas Composition, %                                                                           Superficial Velocity                                Hours      CO      H.sub.2 N.sub.2                                                                            cm/s                                          ______________________________________                                        0-1        75      25       0   20                                            1-7        56      19      20   30                                             7-10      60      20      20   30                                            10-12      52      20      20   30                                            12-25      60      20      20   45                                            ______________________________________                                    

First Stage Product

Total Mass: 20 kg

Average Iron Content: 11%

Average Bulk Density: 0.20 g/cm³

The changes in superficial velocity were used to minimize entrainmentduring the very early part of the run and to promote it during thesecond part. At the end of the run, the reactor contained 8 kg ofrelatively iron rich material in addition to the 10 kg of abradant. Atthe end of the run, the reactor was emptied in preparation for thesecond stage run.

Second Stage Operating Conditions

Temperature: 470° C.

Run Time: 34 hours

Superficial Velocity: 20 cm/s

Abradant: 3.4 kg angular Blastite, 300 micron mean size 6.6 kg angularalumina, 120 micron mean size

Catalyst: 15 kg of material from first stage run, average iron content9%, average bulk density 0.2 g/cm³. Material fed in three 5 kgincrements over first 23 hours of run.

    ______________________________________                                        Gas Composition:                                                                          CO, %   H.sub.2, %                                                                            N.sub.2, %                                        ______________________________________                                                  70    20      10      (first 20 hours)                                        56    20      24      (last 14 hours)                               ______________________________________                                    

Second Stage Product

Total mass: 27 kg

Average Iron Content: 5%

Average Bulk Density: 0.13 g/cm³

The large Blastite abradant provided lower bubbling layer agitation, andthe smaller alumina promoted elutriation. At the end of the run, onlyabout 1 kg of carbon/iron material remained in the reactor.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims shouldnot necessarily be limited to the description of the preferred versionscontained herein.

What is claimed is:
 1. A method for preparing a fibrouscarbonaceous/ferrous group metal material comprising the steps of:(a)introducing a feed gas containing carbon monoxide into a reaction zonehaving a bed containing particulate material to form a fluidized bed,the particulate material comprising a discrete abradant and a discretecatalyst containing ferrous metal, the abradant constituting at least2/3 of the weight of the particulate material, the catalyst catalyzingthe disproportionation of at least a portion of the carbon monoxide toform (i) a reacted gas stream and (ii) a fibrous carbonaceous/ferrousmetal material that forms on the surface of the catalyst, the abradantbeing non-catalytic to carbon deposition and abrading the fibrouscarbonaceous/ferrous metal material from the surface of the catalyst,wherein the feed gas is introduced into the reaction zone (i) at atemperature at least 50° C. lower than the temperature of the reactionzone and (ii) at a sufficient velocity for fluidizing the particulatematerial and so that the reacted gas stream elutriates abraded fibrouscarbonaceous/ferrous metal material from the fluidized bed at a ratesuch that the bed turnover time for carbon is from 2 to 50 hours; (b)maintaining the temperature in the reaction zone from 300° to 700° C.;(c) maintaining the pressure in the reaction zone from about 1 to about10 atmospheres; (d) withdrawing elutriated fibrous carbonaceous/ferrousmaterial from the reaction zone, the withdrawn material comprising atleast 2% by weight ferrous metal and at least 70% weight carbon, thewithdrawn material having a weight average particle size of from about 1to about 50 microns; and (e) introducing catalyst to the reaction zonefor replenishing the ferrous metal withdrawn from the reaction zone aspart of the fibrous carbonaceous/ferrous metal material.
 2. The methodof claim 1 wherein the bed includes a lower ferrous metal-rich regionand an upper carbon-rich region, the abradant in the lower region havinga weight average particle size greater than about 120 microns and theabradant in the upper region having a weight average particle size ofless than about 120 microns.
 3. The method of claim 2 in which theabradant in the lower region is denser than the abradant in the upperregion.
 4. The method of claim 3 in which the density of the abradant inthe lower region is at least 1.2 times the density of the abradant inthe upper region.
 5. The method of claim 2 in which the introducedcatalyst comprises discrete particles having a weight average particlesize of greater than 120 microns.
 6. The method of claim 1 in which thewithdrawn material contains more than 5% ferrous metal.
 7. The method ofclaim 1 in which the fluidized bed is in a reactor having a lowerportion with a first cross sectional area and an upper portion with asecond cross sectional area that is greater than the first crosssectional area, the method including the step of introducingfluidization gas into the upper portion so that the superficial velocityof gas flowing through the upper portion is at least 80% of thesuperficial velocity of the gas flowing through the lower portion. 8.The method of claim 7 in which the fluidization gas is feed gas.
 9. Themethod of claim 1 which includes contacting the abraded fibrouscarbonaceous/ferrous metal material with carbon monoxide for increasingthe carbon-to-ferrous metal ratio in the abraded material before itexits the bed, wherein the ferrous metal of the abraded materialcatalyzes the disproportionation of at least some of the carbon monoxideand wherein additional carbon forms on the abraded material.
 10. Themethod of claim 1 wherein the abradant constitutes from about 2/3 toabout 4/5 by weight of the total weight of the particulate material inthe fluidized bed.
 11. The method of claim 10 wherein the abradant has aweight average particle size of from about 80 to about 120 microns. 12.The method of claim 1 in which the temperature of the feed gas is 250°C. or lower.
 13. The method of claim 1 in which the step of maintainingthe temperature comprises cooling the reaction zone.
 14. The method ofclaim 1 including the step of forming gas bubbles from the feed gas in abubble formation zone for agitating the fluidized bed, the bubbleformation zone comprising fluidized inert particles located proximate tothe location that feed gas is introduced to the reaction zone, the inertparticles being non-catalytic to carbon deposition and having a weightaverage particle size of at least 200 microns.
 15. The method of claim14 in which the inert particles in the bubble formation zone have a bulkdensity of from about 1.4 to about 4 g/cm³ and a weight average particlesize of from about 200 to about 300 microns.
 16. The method of claim 1in which the withdrawn material has a weight average particle size ofgreater than 5 microns.
 17. The method of claim 1 in which thetemperature in the reaction zone is maintained from 400° to 700° C. 18.The method of claim 1 in which the weight average particle size of thecatalyst is less than 100 microns.
 19. The method of claim 1 in whichthe abradant has a weight average particle size of from 80 to 120microns.
 20. The method of claim 1 in which the feed gas containshydrogen and the volume ratio of carbon monoxide to hydrogen is at least1:1.
 21. The method of claim 20 in which the volume ratio of carbonmonoxide to hydrogen in the feed gas is at least 2:1.
 22. The method ofclaim 1 in which the bed turnover time for carbon is less than 25 hours.23. The method of claim 1 in which the material withdrawn from thereaction zone has a bulk density of at least 0.05 g/cm³.
 24. The methodof claim 23 in which the material withdrawn from the reaction zone has abulk density of up to 0.7 g/cm³.
 25. The method of claim 1 wherein thesuperficial velocity of the feed gas through the reaction zone is about40 to about 70 centimeters per second.
 26. The method of claim 1 whereinthe superficial velocity of the feed gas through the reaction zone isabout 10 to about 70 centimeters per second.
 27. A method for preparinga fibrous carbonaceous/ferrous group metal material comprising the stepsof:(a) introducing a feed gas containing carbon monoxide and hydrogeninto a reaction zone having a bed containing particulate material toform a fluidized bed, the volume ratio of carbon monoxide to hydrogen inthe feed gas being at least 2:1, the particulate material comprising adiscrete abradant having a weight average particle size of from 80 to120 microns and a discrete catalyst containing ferrous metal, theabradant being present in an amount of from about 2/3 to about 4/5 byweight of the particulate material, the catalyst catalyzing thedisproportionation of at least a portion of the carbon monoxide to form(i) a reacted gas stream and (ii) a fibrous carbonaceous/ferrous metalmaterial that forms on the surface of the catalyst, the abradant beingnon-catalytic to carbon deposition and abrading the fibrouscarbonaceous/ferrous metal material from the surface of the catalyst,wherein the feed gas has a temperature of 250° C. or less and isintroduced into the reaction zone at a sufficient velocity forfluidizing the particulate material and so that reacted gas streamelutriates abraded fibrous carbonaceous/ferrous metal material from thefluidized bed, the superifical velocity of gas in the raction zone beingfrom about 10 to about 70 cm/s, the bed turnover time for carbon beingfrom 4 to 50 hours; (b) maintaining the temperature in the reaction zonefrom about 400° to about 550° by cooling the reaction zone; (c)maintaining the pressure in the reaction zone from about 1 to about 10atmospheres; (d) withdraswing elutriated fibrous carbonaceous/ferrousmetal material from the reaction zone, the withdrawn material comprisingat least 2% by weight ferrous metal and at least 70% by weight carbon,the withdrawn material having a weight average particle size of fromabout 5 to about 50 microns and a bulk density of at least 0.5 g/cm³ ;and (e) introducing ferrous metal to the reaction zone for replenishingthe ferrous metal withdrawn from the reaction zone as part of thefibrous carbonaceous/ferrous metal material.
 28. The method of claim 27in which the material withdrawn from the reaction zone has a bulkdensity of up to 0.7 g/cm³.
 29. The method of claim 27 wherein thesuperficial velocity of the gas through the reaction zone is about 40 toabout 70 centimeters per second.
 30. A method for preparing a fibrouscarboneous/ferrous group metal comprising the steps of:(a) introducing afeed gas containing carbon monoxide into a reaction zone having a bedcontaining particulate material for forming a fluidized bed, theparticulate material comprising a discrete abradant and a discretecatalyst containing ferrous metal, the abradant constituting at least2/3 of the total weight of the particulate material in the fluidizedbed, the catalyst catalyzing the disproportionation of at least aportion of the carbon monoxide to form (i) a reacted gas stream and (ii)a fibrous carbonaceous/ferrous metal material that forms on the surfaceof the catalyst, the abradant being non-catalytic to carbon depositionand abrading the fibrous carbonaceous/ferrous metal material from thesurface of the catalyst, wherein the feed gas has a temperature of nomore than 250° C. and is introduced into the reaction zone at asufficient velocity for fluidizing the particulate material and so thatthe reacted gas elutriates abraded fibrous carbonaceous/ferrous metalmaterial from the fluidized bed at a rate such that the bed turnovertime for carbon is from 2 to 50 hours; (b) maintaining the temperaturein the reaction zone from about 400° to about 470° C.; (c) maintainingthe pressure in the reaction zone from about 1 to about 10 atmospheres;(d) withdrawing elutriated fibrous carbonaceous/ferrous metal materialfrom the reaction zone, the wtihdrawn material comprising from 3 to 10%by weight ferrous metal, having a weight average particle size of from 1to about 10 microns, and a bulk density of at least 0.05 g/cm³ ; and (e)introducing ferrous metal catalyst to the reaction zone for replenishingthe ferrous metal withdrawn from the reaction zone as part of thefibrous carbonaceous/ferrous metal material, the ferrous metal catalysthaving a weight average particle size of from 0.1 to 100 microns. 31.The method of claim 30 in which the material withdrawn from the reactionzone has a bulk density of up to 0.25 g/cm³.
 32. The method of claim 30in which the material withdrawn from the reaction zone has a bulkdensity of up to 0.7 g/cm³.
 33. The method of claim 32 in which thematerial withdrawn from the reaction zone has a bulk density of up to0.25 g/cm³.
 34. The method of claim 30 wherein the superficial velocityof the feed gas through the reaction zone is about 40 to about 70centimeters per second.